Liver and alcohol breakdown

The liver is your largest internal organ, weighing about 1.5 kg in adults. Your liver sits just under your ribs in the upper, right-hand side of your abdomen. It performs more than 500 functions, including:

processing nutrients from food;

storing energy;

making bile to help with digestion of dietary fats;

filtering toxic chemicals and bacteria from the body;

helping with blood clotting; and

processing medicines.

Your liver is also the main place in your body where alcohol is broken down.

What happens after I drink alcohol?

After you swallow an alcoholic drink, about 25 per cent of the alcohol is absorbed straight from your stomach into the bloodstream. The rest is mostly absorbed from your small bowel. How quickly you absorb the alcohol depends on several factors, including:

the concentration of alcohol in your drink (drinks with a higher alcohol concentration are generally absorbed faster);

whether your drink is carbonated (champagne, for example, is absorbed more quickly than non-sparkling drinks); and

whether your stomach is full or empty (food slows down the absorption of alcohol).

Once alcohol has entered your bloodstream it remains in your body until it is processed. About 90-98 per cent of alcohol that you drink is broken down in your liver. The other 2-10 per cent of alcohol is removed in your urine, breathed out through your lungs or excreted in your sweat.

The average person will take about an hour to process 10 grams of alcohol, which is the amount of alcohol in a standard drink. So if you drink alcohol faster than your body can process it, your blood alcohol level will continue to rise.

How does my liver process the alcohol?

There are 2 ways that alcohol can be processed by your liver. Most alcohol is broken down, or metabolised, by an enzyme in your liver cells known as alcohol dehydrogenase (ADH). ADH breaks down alcohol into acetaldehyde, and then another enzyme, aldehyde dehydrogenase (ALDH), rapidly breaks down acetaldehyde into acetate. The acetate is further metabolised, and eventually leaves your body as carbon dioxide and water.

A small amount of alcohol may be processed using a different set of enzymes in your liver. This alternative pathway, known as the ‘microsomal ethanol-oxidising system’ is mainly used when the level of alcohol in your blood is very high. Regular drinking can increase the activity of this second pathway.

Why can’t some people tolerate alcohol?

Genetic variations can result in the activity of ADH and ALDH (the enzymes needed to process alcohol) varying from person to person. So in different people, the enzymes may be more or less efficient at breaking down alcohol.

About 50 per cent of East Asian people have a genetic variation which means that their ALDH enzyme doesn’t work properly. These people can’t process alcohol in the normal way, and shortly after drinking alcohol their acetaldehyde level rises.

Acetaldehyde is a toxic substance that can cause an unpleasant reaction when it builds up. Symptoms you might experience if your ALDH enzyme does not function properly include flushing of the face, hot sensations, nausea and palpitations (an awareness of your heart beating faster than normal).

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